Sorry if this is mentioned elsewhere, but with with Chinese pools refusing to stop SPV mining, and all these "stress tests" going on right now with the double spending warning up... What are the odds of a double spend occuring? Does a double spend somehow duplicate the Bitcoins being double spent, or does one party get screwed over? Here is a list "The latest 200 double spends (10 Minute Cache)"
https://blockchain.info/double-spends only 1 of which (.5% of list at time of this post) in 2014 and 195 of which (97.5% of list) happened this month! Have the Chinese figured out how to successfully double spend using all their hashpower? Is this what is causing the BTC price to go up, due to manipulation? Should this be means for concern for the entire network, since the biggest pools refuse to comply with stopping SPV mining???
SPV clients trust miners without validating whether the blocks follow the rules of the Bitcoin network.
When BIP 66 was introduced, some miners started to produce invalid blocks [As their backend was allowed to mine on blocks without validating them] but Bitcoin Core 0.9.5+ knows that it is invalid thus rejecting the block and those transactions included in the block would appear unconfirmed to those clients while confirmed to the other SPV clients.
I believe the pools have stopped the SPV mining since they would be suffering loss if they don't stop it. They would be able to double spend their own transaction when they have 51%+ power.